In view of the foregoing, a general object of the invention is to provide a hand-operated, self-powered tool with which laser-welded joints between thin sheets can be opened without the risk of a large amount of contamination.
With hand-operated, self-powered tool according to the invention, a milling cutter is used as the active part engaging the thin sheet, instead of a grinding tool. The milling cutter runs at low rotational speed and generates relatively large scrap shavings, which do not fly very far and which can be removed easily. There is little risk that the produced shavings will burn into the cushioning or the inner lining of the vehicle. The milling tool sits in the casing of a rotary drive that rotates the tool.
To uniquely guide of the milling cutter when it is engaged with the sheet, a foot plate is provided that features a contact surface and a guide edge. The contact surface and the guide edge are located in the immediate vicinity of the milling cutter. The reaction forces that are produced, which can fluctuate very widely under some circumstances, can be introduced into the car body directly from the foot plate. In this case, the penetration depth of the tool is regulated with the help of the contact surface, while the worker has the ability to guide the milling cutter via the edge along the course of the laser-welded seam. The guide edge can be supported either in the lock seam or on the free edge of the car-body part or flange according to the construction of the footplate.
Because the reaction force produced by the cutting force is introduced close to the milling cutter itself, small lever arms are defined, which can be compensated without additional measures by the worker when he holds the rotary drive in his hands. Abrupt changes in the reaction forces are also dampened for these lever ratios, in which even the center of gravity of the rotary drive has a large lever arm compared with the lever arm of the guide edge. This unburdens the worker in that he does not have to react to abrupt changes to the reaction force. The quality of the milled weld seam is accordingly high. In particular, large amounts of material are not removed unnecessarily.
With the guide edge, the worker can guide the milling cutter arbitrarily in terms of the path to be milled. In this respect, the tool needs no additional guide devices for controlling the movement along the weld seam.
Because the rotational axis of the rotary drive is inclined relative to the contact surface defined by the guide plate, the rotary drive itself can be used as a handle for the tool. Additionally, the free space necessary to be able to work the inventive tool into areas of a car-body cutout with small radii of curvature, as is the case, for example, for the corner areas of window cutouts, is created.
The contact surface is preferably a flat surface, which eliminates the risk of tipping that could cause varying penetration depth into the sheet by the milling cutter. The guide edge can define the contact surface on one side and can extend from the contact surface in the direction towards the side of the footplate adjacent to the rotary drive. With such an embodiment of the footplate, the guide edge is guided in the area of the internal corner or channel of a lock seam. In this way, the guide edge can also be rounded when it merges into the contact surface, so that the contact point of the guide edge with the car-body sheet is displaced outwards from the area of the curvature of the lock seam. It is also possible for the guide edge to have a certain spatial separation from the contact surface in the vertical direction, although it is connected directly to the footplate. Such a solution should also be possible using a configuration in which the guide edge defines the contact surface on one side.
Weld seams located in the corner area of a car-body cutout can present problems when the guide edge lies on the side of the rotary drive. The guide edge is also not to be used on the side of the rotary drive when work must be performed at a position of the car body that does not have an internal corner. In such cases, a footplate is preferably used in which the guide edge is lifted from the plane defined by the guide surfaces in a direction pointing away from the drive source. In other words, the rotary drive can be located on one side of the footplate and the guide edge can be arranged on the other side of the footplate. Such a guide edge stops, for example, at a simple bolt that projects from the contact surface.
The guide edge can be a curved edge, for example, with a changing radius of curvature. In this way, the position of the milling cutter can be regulated relative to the reference edge without additional measures by rotation about axes at a right angle to the contact surface. In each case, the reaction force is introduced directly into the car body via the guide edge.
Very favorable work conditions are produced when the rotational axis is inclined by a generally acute angle relative to the plane defined by the contact surface. The intersection point between the rotational axis and the contact surface plane lies on the other side as compared to the rotary drive relative to the holder.
Preferably, a spherical cutter, i.e., a milling cutter with a cylindrical shaft and a spherical cutting head is used as a milling cutter for the hand-operated tool of the invention. This cutting head tends to not get caught in the thin sheet metal even when turned in the plane of the footplate in order to change the distance of the milling cutter from the outer edge or the internal corner of the car-body part.
A compressed-air motor or an electric motor can be used as the rotary drive. In this case, compressed air motors are preferred over electric motors in that they are lighter; however they require a somewhat more expensive energy source.
To generate sufficient cutting speed, the milling cutter is preferably coupled directly to the armature shaft or the rotor of the compressed air motor. In addition, this arrangement has the advantage of saving a lot of space in the area of the milling cutter, so that work can be performed with short clamping lengths. This, in turn, increases the stiffness or vibration resistance of the entire arrangement.
A particularly advantageous and stable connection of the rotary drive to the footplate can be achieved when the rotary drive has an attachment neck coaxial to the casing. The attachment neck can be provided with a cylindrically smooth surface or with an external thread.
The milling depth can be regulated by either shifting the rotary drive along the rotational axis or changing the angle of the rotational axis relative to the footplate.
Advantageously, the footplate sits on a holder, which connects the footplate to the rotary drive. This holder can have an articulated joint for regulating the milling depth.
In the case of a neck provided with threads, the holder has a threaded bore so that the milling depth can be adjusted by screwing the holder back and forth on the neck of the rotary drive. The set screw depth can be fixed with the help of an optional clamping device.
By reading the description of the figures, it will become clear to someone skilled in the art that a series of modifications is possible, which do not have to be described explicitly.